Alkyd polymers are widely used in the coatings industry because of their excellent gloss characteristics and their ability to adhere to various substrates. These qualities are important for industrial applications. However, regulations related to volatile organic compounds (VOCs) have mandated that the coatings industry decrease the VOC content of their products. In some situations this has required a switch from solvent-based coatings to water-based or water-borne coatings. This has led to performance issues.
For example, water-borne alkyds may have a short shelf life due to poor hydrolytic stability. In an effort to improve the hydrolytic stability of water-borne alkyds and to lower the VOC, there has been developed an acrylic modified alkyd dispersion in which a hydrolysis resistant acrylic polymer becomes a “shell” that covers and protects the “core” alkyd from hydrolysis in the water dispersion. Despite success in extending shelf-life and lowering the VOC to about 100 g/l, such acrylic modified alkyd dispersion may demonstrate poor corrosion resistance. Thus, corrosion resistance remains an area in which improvement is desirable.
Another drawback that water-borne alkyd dispersions face is high viscosity. Measures of coating performance, such as drying time and hardness development, are related to the molecular weight of the alkyd polymer. Thus, it is important that the alkyd polymer have sufficient molecular weight. However, a high molecular weight of the alkyd polymer typically leads to high viscosity for the alkyd dispersion. Processing an alkyd dispersion with a high viscosity may be difficult. However, lowering the amount of alkyd polymer in the dispersion in order to lower the viscosity may result in low resin solids in the alkyd dispersion. Neither of these situations may be desirable. Additionally, alkyd dispersion viscosity may be exacerbated for low VOC alkyd dispersions.
In order to address the issue of high viscosity and low resin solids, formulators have added surfactants to water-borne, low VOC alkyd dispersions. Surfactants have proven helpful to lower the dispersion viscosity for coating applications. Formulators have added surfactants as internal surfactants (i.e., the hydrophilic moiety of the surfactant is reacted with the alkyd polymer). Polyalkylene oxides such as polyethylene oxide and polypropylene oxide have been typically used as internal surfactants.
In another approach to prepare low VOC alkyd product, alkyd emulsion has been introduced that adopts external surfactants (i.e., the surfactant is mixed or otherwise physically blended with the alkyd polymer to form an emulsion). Unfortunately, the presence of a water-sensitive hydrophilic moiety and/or surfactant in the alkyd dispersion and alkyd emulsion has led to a compromise in some of the coating properties of the coatings made with these alkyd products. For example, corrosion resistance and QUV resistance have suffered as a result of using internal and external surfactants in the alkyd dispersion and alkyd emulsion respectively. Corrosion resistance and QUV resistance are important in maintaining coating integrity in outdoor applications.
Further information is described in U.S. Pat. No. 3,639,315, EP application Nos. 2481763 A1 and 2444436 A1, International patent application publication Nos. WO 2004/060949 A1 and WO 2008086977 A1, and Chinese patent application No. CN102108246 A, in the name of Faming Zhuanli Shenqing.
Thus, a need exists for a water-borne, low VOC alkyd product that does not contain internal or external surfactants and has a workable viscosity and excellent coating performance.